This invention relates to a system and a method for continuously preventing bridging between filament draw nozzles used in the production of nonwoven fabrics.
Draw nozzles are commonly used in directing filaments to a desired location for nonwoven web formation. Compressed air generally supplied to the nozzles serves as an entraining medium for the filaments. Examples of prior art filament draw nozzles are described in U.S. Pat. No. 3,338,992 and U.S. Pat. No. 3,341,394, both to Kinney; Dorschner et al. patents, U.S. Pat. No. 3,665,862 and U.S. Pat. No. 3,692,618; U.S. Pat. No. 3,754,694 to Reba; and Reba patent application U.S. Ser. No. 192,973, now U.S. Pat. No. 4,332,027.
Filament draw nozzles such as described in U.S. Ser. No. 192,973 receive a filament bundle which is drawn downwardly from a spinning plate through a cooling chamber. Filament draw nozzles are located below filament spinning systems and are typically arranged in rows above a moving formation wire. The width of each of these rows depends on the width of the nonwoven fabric to be formed. The rows of draw nozzles extend in a cross-machine direction with respect to the formation wire. Adjacent draw nozzles are located at a distance one from the other which will facilitate uniform, nonwoven web formation, particularly in the machine direction, and avoid a substantial degree of streaking.
A combination of factors such as cooling air turbulence, excessive cross-flow velocity, improper air temperature, and/or various polymer melt properties, causes filament breakage prior to the filaments entering the nozzle throat. The broken filaments are suspended between adjacent nozzles causing "filament bridging" to occur. Once initiated by a single filament, bridging causes subsequently produced filaments to be continually collected until a filament aggregate structure is formed. When this snake-like structure dislodges itself from the bridged position, a phenomenon known as "filament shedding" occurs. This snake-like filament structure then passes through the nozzle system and causes a defect in the subsequently produced nonwoven web.
Another problem associated with filament bridging is defined as "filament diversion". In this latter situation, filaments from adjacent spinning systems are diverted into a single filament draw nozzle by the bridging filaments which act as a unidirectional flow path for the downwardly drawn filaments. Filament diversion can cause plugging of the draw nozzles to which all of the filaments are diverted, as in the case of the system described in the Dorschner patents, and/or streaking of the nonwoven web.
Therefore, it is an object of this invention to produce a system which will eliminate, or at least minimize, filament bridging across adjacent draw nozzles.